The invention relates to methods and devices for assessing viscoelastic properties of soft tissues. In particular, the invention relates to using aspiration methods to detect elasticity, viscosity, creep and other properties of accessible living tissues such as skin, cervix, vaginal wall, etc.
Mechanical properties of skin (e.g., elasticity of skin) may change due to disease, stress, or dehydration. When the body becomes dehydrated as a result of diseases such as those that cause diarrhea or reduced liquid intake such as famine or marathon running, the skin becomes “doughy” and does not snap back when pinched. In a test for dehydration called the “pinch test” or “turgor test,” the skin is grasped and pulled up in a pinch-like manner and then released. Healthy skin will quickly snap back to its undeformed state, whereas dehydrated skin returns to its undeformed state slowly. Such conventional test is subjective and inaccurate. Objective determination of skin elasticity is important for detecting a state of dehydration as well as diagnosis of other pathological conditions.
Characterizing viscoelastic properties of other human soft tissues is clinically important as well. One such tissue is female uterine cervix. The occurrence of cervical ripening before 34 weeks of gestation leading to preterm delivery represents a serious medical problem. Preterm delivery is a major cause of perinatal morbidity and mortality. About 12.5 percent of babies (more than half a million a year) in the United States are born prematurely. For reasons that doctors do not fully understand, the rate of premature birth has increased by more than 30 percent since 1981. Premature babies are at increased risk for newborn health complications, as well as lasting disabilities, such as mental retardation, cerebral palsy, lung and gastrointestinal problems, vision and hearing loss, and even death.
The uterine cervix has to provide mechanical resistance to ensure a normal development of the fetus. Cervical softening occurs progressively in the last one-third of pregnancy. The process of cervical ripening, consisting of softening of the connective tissue components, is not easily identifiable with present methods. Objective quantitative assessment of cervical ripening will allow dispensing of therapy for preterm labor. Specific defects in cervical ripening will then be diagnosed and treated.
Another area in need of an objective device and method for characterization of soft tissue is in detection of pelvic organ prolapse, a major cause of female incontinence. Pelvic organ prolapse (POP) is a highly prevalent condition affecting at least 50% of women in the US at some point during their lifetimes. One recent study including 27,342 women revealed that 40% percent of women aged 50 to 79 years have some form of pelvic organ prolapse. Some loss of utero-vaginal support occurs in most adult women. However, the true etiology of prolapse and differences seen among individuals are not entirely understood. Changes in the elasticity of the vaginal walls, connective support tissues, and muscles are thought to be significant factors in the development of pelvic organ prolapse. The high incidence of POP dictates the need for effective means of its early detection and characterization as well as evaluating the risk of further prolapse development.
Aspiration methods for assessment of elasticity of skin and other soft tissues are generally known. Typically, a device forms a cavity over a tissue sample. Air is then aspirated causing the tissue to be drawn into the cavity. Extent of tissue prolapse into the cavity is measured by various mechanical, optical or other means. Tissue elasticity is then determined based on the degree of such prolapse and the level of vacuum achieved by the device. Examples of prior art attempts at various devices based on this aspiration method are found in U.S. Pat. Nos. 4,365,638; 4,976,272; 5,278,776; 7,556,605; US Patent Application Publication No. 2008/0234607 and the PCT Publication No. WO 03/105689. These devices however lack the ability for a comprehensive assessment of tissue which goes beyond simple elasticity measurements.
Other areas of interest for detection of tissue elasticity include intraoperative detection of lesion boundaries during open surgery procedures.
The need therefore exists for improved methods and devices to measure various viscoelastic properties of soft tissues such as elasticity modulus, tissue viscosity and tissue creep.